Using Different Doses of Active Vitamin D Combined With Neutral Phosphate in Children With X-linked Hypophosphatemia

Comparing the Effectiveness of High or Low Dose of Active Vitamin D Combined With Neutral Phosphate in Children With X-linked Hypophosphatemia

X-linked hypophosphatemia (XLH) is the most common form of heritable rickets. Current treatments include active vitamin D metabolites (e.g. calcitriol) and phosphate salts. There is no consistent weight-based dosing of calcitriol and phosphate now. The primary objective of this study is to establish the efficacy of different dose of calcitriol combined with neutral phosphate in children with XLH.

Inclusion Criteria:

• Male or female, aged 1-12 years, inclusive
• Diagnosis of XLH by clinical features: serum phosphorus level < 2.5 mg/dl; ALP?; RSS total score ≥2; bowed legs; short stature; family history with appropriate X-linked inheritance
• Meet at least one of the following: confirmed Phosphate regulating gene with homology to endopeptidases located on the X chromosome (PHEX) mutation in the participant, or serum FGF23 level >30 pg/ml (Kainos assay)
• Willing to participate the study, and provide an informed consent
• Able to complete all aspects of study and adhere to the visit schedule

Exclusion Criteria:

• Use of growth hormone within 12 months before first visit
• Height >50 percentile for age and sex specific data
• Presence of nephrocalcinosis or nephrolithiasis
• Serum intact parathyroid hormone level>170 pg/ml
• Plan to receive orthopaedic surgery in 12 months
• Poor compliance
• Use of gonadotropin-releasing hormone therapy right now
• Use of aluminium hydroxide, steroid, acetazolamide or thiazide drugs within 7 days before first visit
• Not be fit to participant in the study, by the judgement of investigators